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Old 11-16-2016, 10:53 AM   #675 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
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TDi - '04 VW Golf
90 day: 51.75 mpg (US)
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Originally Posted by basjoos View Post
I made a trip up to the NC mountains a few weeks back and saw the effect that altitude has on mpg. At 400 feet elevation at 55mph, 15" of manifold pressure, and 85 degrees my SuperMID shows 100mpg. At 2100 feet elevation those same parameters show close to 120mpg. The mpg improvement would be due to a combination of reduced aero drag in the thinner air and the 15" of manifold pressure at 2100 feet elevation resulting in a wider open throttle plate for reduced pumping losses. I wonder what it would show at 6000 feet, not that there are any flat, straight road stretches to try this on in the eastern US.
I have a stretch of road between Steamboat Springs and Laramie WY where the elevation is over 8,000 feet for much of the trip. In that thin air I can hit 70@70 where mpg and speed are the same. At lower elevations I have to drive much slower to come close to those numbers. And the diesel doesn't have a throttle plate like a gas engine.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun
make NOx not Carbon

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.
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